The present invention relates to magnetic sensor for reading data signals stored in a magnetic recording medium.
A magnetic read transducer called an MR (magnetoresistive) effect sensor or an MR effect head is conventional and capable of reading data out of a magnetic surface with high liner density, as reported in the past. The MR effect sensor or head senses a magnetic field signal in terms of the variation of resistance which is the function of the intensity and direction of a magnetic flux sensed by a reading device. The conventional read transducer is based on an AMR (Anisotropic Magneto Resistance) effect, i.e., the fact that one component of the resistance of a reading device varies in proportion to the square of the cosine of an angle between the direction of magnetization and the direction of a sense current flowing through the reading device.
For details of the AMR effect, reference may be made to D. A. Thompson et al. xe2x80x9cMemory, Storage, and Related Applicationsxe2x80x9d, IEEE Trans. on Mag. MAG-11. p. 1039 (1975).
It is a common practice with a magnetic head utilizing the AMR effect to apply a longitudinal bias magnetic field for reducing Barkhausen noise. To apply the vertical bias magnetic field, use is sometimes made of FeMn, NiMn, nickel oxide or similar antiferromagnetic material. There has recently been reported a more noticeable MR effect, i.e., the fact that the resistance of a laminate magnetic sensor is ascribable to the spin-dependent transfer of conductive electrons occurring between magnetic layers via a nonmagnetic layer and spin-dependent diffusion occurring at an interface between layers due to the above transfer. This kind of MR effect is generally referred to as, e.g., a macro MR effect or a spin valve effect.
The above MR sensor is formed of a suitable material and has higher sensitivity than a sensor using the AMR effect and therefore noticeably varies in resistance. In this kind of MR effect sensor, two ferromagnetic layers are separated from each other by a nonmagnetic layer. Resistance in the plane between the two ferromagnetic layers varies in proportion to the cosine of an angle between the magnetization directions of the ferromagnetic layers.
Japanese Patent Laid-Open Publication No. 2-61572, for example, discloses a laminate magnetic structure featuring high MR variation based on the antiparallel alignment of magnetization in a magnetic layer. As for materials usable for the laminate structure, the above document mentions ferromagnetic transition metals and alloys. Further, the document teaches a structure in which an antiferromagnetic layer is added to one of at least two ferromagnetic layers, and indicates that FeMn is feasible for the antiferromagnetic layer.
Japanese Patent Laid-Open Publication No. 4-358310 proposes an MR sensor including two thin ferromagnetic layers separated from each other by a thin nonmagnetic metal layer. When no magnetic field is applied to this MR sensor, the magnetization directions of the two ferromagnetic layers are perpendicular to each other. Resistance between the two non-coupled ferromagnetic layers varies in proportion to the cosine of the angle between the above magnetization directions independently of the direction of current flowing through the sensor.
Japanese Patent Laid-Open Publication No. 6-203340 discloses an MR sensor also based on the above effect and including two thin ferromagnetic layers separated by a nonmagnetic thin metal layer. When the outside magnetic field is zero, the magnetization of an adjoining antiferromagnetic layer remains perpendicular to the magnetization of the other ferromagnetic layer.
Japanese Patent Laid-Open Publication No. 7-262529 teaches an MR effect element or spin valve made up of a first magnetic layer, a nonmagnetic layer, a second magnetic layer, and an antiferromagnetic layer. For the first and second magnetic layers, use is made of CoZrNb, CoZrMo, FeSiAl, FeSi or NiFe with or without Cr, Mn, Pt, Ni, Cu, Ag, Al, Ti, Fe, Co or Zn added thereto.
Japanese Patent Laid-Open Publication No. 7-202292 proposes an MR effect film including a plurality of magnetic thin films laminated on a substrate and separated by a nonmagnetic layer. An antiferromagnetic thin layer adjoins one of soft magnetic thin films adjoining each other with the intermediary of a nonmagnetic thin film. Assume that a bias magnetic field applied to the antiferromagnetic thin film is Hr, and that the coercive force of the other soft magnetic thin film is HeZ. Then, a relation Ho2 less than Hr holds. The antiferromagnetic material is implemented by at least one of NiO, CoO, FeO, Fe2O2, MnO and Cr or a mixture thereof.
Japanese Patent Laid-Open Publication No. 8-127864 teaches an MR effect film similar to the above film, except that the antiferromagnetic thin layer is implemented as a superlattice consisting of at least two of NiO, NixCo1-xO and CoO.
Further, Japanese Patent Laid-Open Publication No. 8-204253 discloses an MR effect film similar to the above film except that the antiferromagnetic layer is a superlattice consisting of at least two of NiO, NixCo1-xO=(x=0.1-0.9), and CoO. In the superlattice, the ratio of Ni to Co in the number of atoms is greater than 1.0 inclusive.
As for an effect MR element basically consisting of a free magnetic layer, a nonmagnetic layer, a fixed magnetic layer and a fixing magnetic layer, it is preferable that the free magnetic layer has an easy axis of a uniaxial magnetic anisotropy substantially perpendicular to the magnetization direction of the fixed layer.
The above type of MR effect element should preferably be designed and used such that the magnetization direction of the free magnetic layer and that of the fixed layer are substantially perpendicular to each other in a zero magnetic field. At this instant, if the easy axis direction of the free magnetic layer and the magnetization direction of the fixed layer make an angle close to a right angle, then a magnetic field (leakage magnetic field from a record mark on a magnetic recording medium with respect to the operation of a read head) is applied in the hard axis direction of the free magnetic layer. This successfully reduces the coercive force of the free magnetic layer and thereby reduces the hysteresis of the R-H loop when the MR effect element is used as a read sensor. It is therefore possible to reduce the noise of a reproduced signal.
However, many of the conventional MR elements use an antiferromagnetic material for the fixing layer. Further, many of antiferromagnetic materials expected to be put to practical use as a fixing layer must be heated at temperature above 200xc2x0 C. in a magnetic field parallel to the magnetization direction of the fixed layer, so that a sufficient exchange coupled magnetic field can be applied to the fixed layer.
In each of the conventional MR effect element of the type described, the antiferromagnetic layer is formed after the formation of the free magnetic layer, nonmagnetic layer, and fixed magnetic layer. Therefore, the above heat treatment acts not only on the fixed magnetic layer and fixing magnetic layer but also on the free magnetic layer. Consequently, the easy axis of the uniaxial magnetic anisotropy of the free magnetic layer is oriented parallel to the direction of the magnetic field, i.e., the magnetization direction of the fixed magnetic layer. This increases the coercive force of the free magnetic layer and thereby increases noise when the MR effect film is used as a sensor.
Technologies relating to the present invention are also disclosed in, e.g., Japanese Patent Laid-Open Publication No. 9-199326.
It is therefore an object of the present invention to provide an MR effect element capable of reducing the coercive force of its free magnetic layer and therefore the hysteresis of the R-H loop, and an MR effect sensor and an MR sensing system using the same and featuring a desirable noise characteristic.
In accordance with the present invention, in an MR effect element, a laminate film is implemented by a unit consisting of an Si layer, a metal lower layer, a free magnetic layer, a nonmagnetic layer, a fixed layer, and a magnetic fixing layer.
Also, in accordance with the present invention, in an MR effect element, a laminate film is implemented by a unit consisting of an Si layer, a diffusion control layer, a metal lower layer, a free magnetic layer, a nonmagnetic layer, a fixed layer, and a magnetic fixing layer.